Two-stage sonic atomizing device



Nov. 3, 1970 c. F. PECZELI ETAL 3,537,650

TWO-STAGE some ATOMIZING DEVICE Filed April 14, 1969 3 SheetsSheet 1INVEN'I'OR. CHARLES F. PECZELI EDW RD T YRCZ BY/ PATENT' AGENT Nov. 3,1970 c, z ETAL 3,537.650

I TWO-STAGE SONIC ATOMIZING DEVICE 7 Filed April 14, 1969 3 Sheets-Sheet:2

STEPPED VORTEX CHAMBERS GEOMETRY FIGA G INVENTORS= CHARLES E PiQLEu pEDWARD T BY ,1

Nov. 3, 1970 c. F. PECZELI E 7,

TWO-STAGE some ATOMIZING DEVICE Filed April 14, 1969 5 Sheets-Sheet 5STEPPED VORTEX CHAMBERS ENERGY vs LOCATION an I 45$ R LEGEND I DM 3.3m

2 D/d G 40 0m 1.5

'3} n PRESSURE i3 (POTENTIAL) ENERGY 25 3 AVAILABLE w 5 ENERGY 2 III IKINETIC ENERGY 6 l5 l 2' I0 I I I 3 I I J U 0- I 3' I I I 0* v d".lNLET-.-- DISCHARGE FIG. 9

l VENTORS= CHARLES F. ECZELI AND EDWMN TI TYKCL MAW United States Patent3,537,650 TWO-STAGE SONIC ATOMIZIN G DEVICE Charles F. Peczeli,Clarkson, Ontario, and Edward T. Tyrcz, Toronto, Ontario, Canada,assignors to Gulf Oil Canada Limited, Toronto, Ontario, CanadaContinuation-impart of application Ser. No. 650,342, June 30, 1967. Thisapplication Apr. 14, 1969, Ser.

Int. Cl. Bb 7/10 US. Cl. 239-405 5 Claims ABSTRACT OF THE DISCLOSURE Aliquid atomizer having a cylindrical vortex chamber with at least onetangential inlet, and a concentric outlet tube. A substantially sharpcorner marks the transition from the chamber to the outlet tube and thechamber wall through which the outlet tube opens is substantially normalto the latter. A liquid feed tube is provided axially within the outlettube and has a port for expelling a jet of liquid centrifugally towardthe outlet tube Walls.

This invention relates to devices for atomizing liquids, and has to doparticularly with the application of the rotary vortex to the problem ofliquid atomization. A particular application of the device to which thisinvention is directed relates to the atomization of fuel oils.

This application is a continuation-in-part of US. patent application No.650,342 Two-Stage Sonic Atomizing Device, Charles F. Peczeli and EdwardT. Trycz, filed June 30, 1967, now abandoned.

Before going into the specific objects and advantages of the presentinvention, it will be helpful to discuss several theoretical pointsrelating to the proper operation of fuel oil burners.

Most kinds of oil fuel require approximately 14.5 pounds of combustionair to burn completely 1 pound of fuel. This ratio is referred toscientifically as the stoichiometric ratio, and its significance issimply that it takes about 14.5 pounds of air to provide suflicientoxygen to burn all of the carbon, hydrogen and other combustibles in 1pound of fuel oil. In order to ensure that the fuel oil is completelyburned, however, it is standard practice to provide an excess amount ofair at the point of burning. This is done because no fuel atomizer isable to create a nebulous spray whose burning characteristics are thesame as if the fuel oil were vaporized, and because complete andhomogeneous mixing of the combustion airwith the atomized fuel is neverfully attained. When the necessary excess air is greater than about 5%of the stoichiometric amount, the result will be a substantial amount ofoxygen exiting from the burning chamber along with the combustion gases.The problem here arises because of the sulphur present in the oil. Mostof the sulphur burns to S0 but if excess oxygen is present, a portion ofthe sulphur will burn to S0 and the latter will combine with watervapour to form sulphuric acid, H 80 which is corrosive to metalsurfaces, etc. However, when the stoichiometric excess air is limited tothe area of 5% or less, there is a considerable reduction in the S0production, and the evolution of H 80, substantially disappears.

In order to permit the stoichiometric excess air to be limited to thearea of 5% or less, it is necessary to set up high recirculation ratesin the combustion chamber, so that some of the hot combustion gases willbe caused to recirculate back to the point at which the cool air-fuelmixture enters. The combustion gases mix with the incoming air-fuelmixture, promoting a high rate of evaporation and rapid combustion, andthus improving the efiiciency of the burning.

One way of promoting a high recirculation rate of the combustion gasesis to provide a fuel atomizer which has a wide spray angle.

In view of the above, it is one object of this invention to provide anatomizer which is capable of producing a wide-angle atomized spray ofliquid.

A further object of this invention is to provide an atomizing deviceutilizing the principle of gas-vortex atomization, which is capable ofutilizing a high-pressure vortex medium, and can efiiciently atomizecertain thick, viscous liquid, such as the heavier fuel oils and pitchfuels.

Essentially, the apparatus of this invention achieves the above objectsby utilizing a particular rotary-vortex chamber design to produce ahigh-speed rotary vortex of an atomizing medium such as steam or air, incombination with a two-stage atomizing technique carried out at thedownstream end of an outlet tube in which the atomizing medium isrotating. The special design of the vortex chamber and outlet tubeproduces a desired ratio of axial to tangential velocity within theoutlet tube and results in a wide-angle spray cone, while the two-stageatomizing technique ensures that a high degree of comminution andnebularization of the heavy viscous oil will occur.

More particularly this invention provides a liquid atomizer comprising:means defining a substantially cylindrical chamber having a forward endwall and a rearward end wall, a cylindrical outlet nozzle defining atleast part of said forward end wall and having an outlet bore ofdiameter less than that of said chamber and extending co-axially awayfrom the chamber, the forward end wall and the outlet bore meeting todefine a substantially sharp corner around which gas must pass whenmoving from said chamber into said outlet bore, at least onesubstantially tangential inlet to said chamber, means for causing a gasto pass under pressure through said inlet and into said chamber so as toset-up a rotating vortex in said chamber, the said pressure beingsufiicient to cause the rotational speed of the gas in the chamber at aradius equal to that of the outlet bore to be greater than sonic,whereby the gas exits from the chamber through the outlet bore whilerotating at a speed greater than sonic and establishes a rotating vortexalong the outlet bore the speed of which decreases, due to friction, tosubstantially sonic velocity near the downstream end of the outlet bore,and liquid feed means located substantially axially within said outletbore for expelling at least one jet of liquid centrifugally into thevortex where the latter has substantially sonic velocity.

One embodiment of this invention is shown in the accompanying drawings,in which like numerals refer to like parts throughout the several views,and in which:

FIG. 1 is an axial sectional view through the nozzle of an oil burnerequipped with a vortex-type atomizer;

FIG. 2 is a transverse sectional view taken at the line 2-2 in FIG. 1;

FIGS. 3, 4 and 5 are diagrammatic axial views of three vortex chamberdesigns, utilized in a discussion of comparative energy requirements;

FIGS. 6, 7 and 8 are axial sectional views of the vortex chamber designsshown in FIGS. 3, 4 and 5, respectively; and

FIG. 9 is a graph showing energy conversion, for the three vortexchamber designs shown in FIGS. 3 to 8, as the atomizing medium passesfrom the tangential inlet through the device to the downstream end ofthe outlet tube.

FIG. 1 shows an oil burner nozzle 10, which includes a cylindricalatomizer mounting sleeve 12 into the open end of which is threaded aconical vertex body 14. The

apex of the conical vortex body 14 has an axial bore 15 which is widenedat 16 to define an annular shoulder 17. A gas nozzle 18 is shaped to fitsnugly within the bore 15 and the widened portion 16 in the conicalvortex body, and is held in position by a vortex chamber housing 20which is threaded into the conical vortex body 14.

A feed tube 22 extends in sealed relationship through an axial aperture23 in the vortex chamber housing 20, and passes centrally through thevortex chamber 21 to enter concentrically a co-axial outlet bore 24 inthe gas nozzle 18. The diameter of the outlet bore 24 is greater thanthe outside diameter of the feed tube 22, such that an annular space 26is defined therebet-ween. At its upstream end, the feed tube 22 isconnected, by welding or press-fitting, to a tubular connecting element28 which is in turn connected to a fuel line (not shown) which deliversfuel under pressure to the connecting element 28 and thence to the feedtube 22. The connecting element 28 is secured centrally through apartition 30 which is threaded into the upstream end of the conicalvortex body 14.

A pressurized gaseous medium is delivered to the nozzle through a line(not shown) located inside the atomizer mounting sleeve 12 and fastenedin eccentric port 31. For the remainder of this description, the mediumis considered to be steam, although other gases can be used, as is laterdiscussed. The steam passes into an antechamber 32 defined by thepartition 30, the conical vortex body 14 and the vortex chamber housing20. From the antechamber 32 the pressurized steam enters the vortexchamber 21 through a tangential inlet 34 constituted by a bore holedrilled through the wall of the vortex chamber housing 20, as shown inFIGS. 1 and 2.

Because of the tangential orientation of the inlet 34, the steam rotateswithin the vortex chamber 21 in a counter-clockwise sense as seen inFIG. 2. The steam exits from the vortex chamber 21 by way of the annularspace 26 defined between the outlet bore 24 and the feed tube 22. Thesteam, in progressing from the periphery of the vortex chamber 21 towardits centre, undergoes an increase in rotational speed, the increasevarying inversely with the square root of the radius. The steam passesinto the outlet bore 24 and continues to spin at this higher rotationalspeed as it passes along the outlet bore 24 slowing slightly due tofriction, and it finally spins out into the open at the right-hand endof the outlet bore 24.

It is possible, of course, to provide any number of tangential inlets34, provided their total cross-sectional area is suited to the requiredflow. Also, a slight deviation from the strictly tangential direction isunlikely to have a significant effect on atomization.

This invention provides a two-stage atomization of the liquid to beatomized. The first stage involves forcing the fuel under pressurethrough one or more restricted ports 36 drilled in the periphery of thefeed tube 22. The downstream end of the feed tube 22 is closed as shown,and the ports 36 are drilled in the feed tube 22 closely adjacent theclosed downstream end. The ports 36 function as nozzles which expel thinjets of the liquid centrifugally outwardly into the periphery of thevortex created by the spinning steam. Because of the high rotationalspeed of the vortex, most of the steam is thrown outwardly and forms arotating film or layer adjacent the walls of the axial bore 24. As thethin jets of the liquid impinge upon the rotating steam layer, they arefurther broken up, and more finely atomized.

To achieve the best atomization, the size, number, orientation and axialposition of the ports should be properly selected. The size of the portsshould be such that there is no danger of the liquid clogging orblocking the ports. The number of ports should be such that the requiredliquid flow is achieved at the desired pressure. The orientation of theports, although here considered to be radial, can also be partially orfully tangential to the feed tube 22 and/or tilted in the axialdirection at an angle between 0 and where conditions warrant it. Evenangles exceeding 90 (i.e. the liquid jet is directed, partially, againstthe flow of the vortex medium) may be of advantage under certaincircumstances. As used in this disclosure and in the appended claims,the word centrifugally, as applied to the ports 36 and to the directionof the liquid sprayed from the feed tube 22, is meant to include alltangential angles and all axial inclinations. The location of the portsis dependent upon several considerations. Firstly, the ports should beinside of the outlet bore 24 to ensure that the liquid particles spend along enough time in the region of violent disturbance to become properlyatomized. However, since the liquid particles are swirled around in anever increasing spiral path due to both the radial component of liquidvelocity and the centrifugal force, the ports 36 must be close enough tothe downstream open end of the annular space 26 to ensure that most ofthe particles leave the nozzle before they contact the walls of theoutlet bore 24. The presence of the rotating layer of steam adjacent thewall of the outlet bore 24 helps to ensure that contact between theliquid particles and the wall will be minimal.

Although in the embodiment shown, the ports 36 are all at the same axiallocation, it is conceivable that two or more sets of ports could beprovided at different axial locations, or that the individual portscould be arranged along the feed tube 22 in a random distribution, bothaxially and radially.

It has been found helpful to provide a slight outward conical taper 38at the downstream end of the outlet bore 24. A preferred angle for theconical taper is 30, although this is not critical.

A discussion now follows of the reasons why an abrupt and clearlydefined step between the vortex chamber and the outlet tube isconsidered an essential part of this invention.

Firstly, from the point of view of efliciency, it is considered that theatomizing medium should be moving at sonic velocity at the point ofatomization. Supersonic velocities, as a rule, generally involve heavyenergy losses, while subsonic velocities require an unduly highconsumption for a given energy requirement.

Secondly, in order to achieve an acceptable recirculation pattern of theatomizing medium-fuel spray components within the combustion chamber, itis necessary to ensure that the ratio of tangential to axial velocity atthe discharge is in the neighbourhood of 1:1 or higher.

Thirdly, the layer of the atomizing medium in the discharge of theoutlet bore, described above, must be sufficiently thick to prevent thepenetration of the fuel, since penetration leads to agglomeration on theinside wall, and thus to the formation of large particles. It will beobvious, then, that with a 1:1 velocity ratio, there will be amathematical inter-relationship between the diameter of the dischargenozzle, the flow rate of the atomizing medium, and its axial velocitycomponent.

The energy requirement, in B.t.u.s per pound of atomizing medium, can beminimized by selecting a D/d ratio within a given range, where D is thediameter of the vortex chamber, and d is the diameter of the outlet bore24.

To illustrate these points, attention is directed to FIGS. 3 to 9. FIGS.4 and 7 show the comparative diameters in an actual experimentalprototype which was built and tested under working conditions. The D/ dratio was 3.312, and the actual dimensions of the prototype were asfollows:

Vortex chamber diameter, D=3.312 inches.

Outlet bore diameter, d=1.000 inch.

The vortex chamber had six tangential inlets, each one being 0.125 inchin diameter.

Air was delivered to the tangential inlets at 48 p.s.i.g. pressure andat negligible velocity, and the transforma tions of the total availablepressure energy as the air travelled through the prototype wasdetermined primarily on the basis of pitot tube measurements, andplotted as the solid line in FIG. 9. Attention is now directed to FIG.9.

In FIG. 9, the total energy available in the pressurized medium prior toentering the tangential inlets is indicated by the upper circled dotwith the number 1. At this point, the energy available in thepressurized medium is 42 /2 B.t.u.s per pound. At this point, the mediumis considered to be motionless, and so the kinetic energy is zero, asshown by the circled dot at the bottom bearing the number 1.

As the medium passes through the tangential inlets to the position 2(see FIG. 4) where it is about to enter the vortex chamber, it isaccelerated to 880 feet per second, and there is a slight loss inavailable energy on account of friction. This loss of available energyis shown by the drop in the upper line to the circled dot numbered 2, atwhich the total available energy is reduced to 41.5 B.t.u.s per pound.Frictional losses account for the 1 B.t.u. per pound difference. At thesame time, the kinetic energy increases as shown by the steep rise inthe bottom line from 1 to 2. The pressure energy in the air at thispoint is represented by the distance between the two dots marked 2, butthe kinetic energy is shown to be about 15.5 B.t.u.s per pound.

The air next enters the vortex chamber, and in doing so passes frompoint 2 to point 3 in FIGS. 4 and 7 and in the graph of FIG. 9. Due tothe sudden change of cross-section, and also to the change of direction(from straight to rotation), there is an appreciable energy loss. It isseen in FIG. 9 that the irreversible frictional losses have reduced thetotal available energy to about 34 B.t.u.s per pound, that the pressureenergy available has been reduced slightly, and that the kinetic energyhas been reduced significantly.

The rotating air next moves spirally inwardly toward the centre of thevortex chamber, and its kinetic energy increases in inverse ratio to thediameter. The axial component is zero, the radial component isnegligible, and the tangential component increase from 666 feet persecond on the periphery to 1215 feet per second on the one inch diameterline. This stage is shown in the FIGS. 4 and 7 and in the graph of FIG.9 as a progression from point 3 to point 4. Irreversible frictionallosses result in a slight reduction in the total available energy toabout 31.3 B.t.u.s per pound, while nearly all of the available pressureenergy is converted to kinetic energy through the increase of speed, aswill be seen by the closeness of the two points marked 4 in FIG. 9.

The next stage is the entry of the rotating air into the outlet bore 24,and at this stage a part of its tangential velocity is converted toaxial velocity. In this process, the energy loss is appreciable, as canbe seen by the steep drop of the two lines 4-5 in FIG. 9.

As the air moves along the outlet bore from point to point 6, it isstabilized. Friction losses, however, increase the volume of the air byheating it and causing its pressure to drop, and thus more tangentialvelocity is converted into axial velocity.

At stage 6, representing the divergent section of the outlet bore, theratio of tangential velocity to axial velocity becomes constant. In theatomizing section the air velocity was found to be sonic at 1,046 feetper second, with a tangential component of 768 and an axial component of538 feet per second. Virtually all of the air is discharged on theperiphery, in a layer of 0.10 inch thickness. In the central core, thedensity is small and the axial velocity is negligible.

The following discussion relates to vortex atomizers with different D/ dratios. It was assumed that these must match the prototype describedabove in capacity and in the quality of atomization, and it wastherefore assumed that identical conditions would be required downstreamof stage 4. It was also assumed that the diameter of the outlet borewould be the same. Starting with these assumptions, the necessary graphpoints were calculated backwards from stage 4 for a D/d ratio of 1.5 andfor a D/d ratio of 6.

For the casein which the D/ d ratio is 1.5 (FIGS. 5 and 8), the increaseof velocity in the process 3-4 (the radial inward movement in the vortexchamber) will be small. To make up for this, the discharge velocity inthe tangential inlets (process 1-2) must be significantly higher, andworks out to be in the neighborhood of Mach 1.5. But, if this very highvelocity stream enters a smaller diameter vortex chamber, the energylosses in the process 2-3 will be extremely high. Thus, the intialenergy requirement in B.t.u.s per pound, must be higher than that forthe tested prototype worked out above which had a D/d ratio of 3.312.Refer in FIG. 9 to the broken lines identified by the circled numeralswith asterisks.

Conversely, if the diameter of the vortex chamber is in a larger ratioto the outlet bore than is the case with the prototype described above,for example, 6 inches to 1 inch (FIGS. 3 and 6), then the velocityincrease in the process 3-4 is higher. To compensate for this, thedischarge velocity from the inlet (process 1-2) is proportionatelylower. But, since part of the work of converting pressure to kineticenergy was transferred from a more efficient to a less eflicientprocess, the required supply pressure is higher, and thus the requiredenergy content in B.t.u.s per pound of the atomizing medium must behigher. Refer in FIG. 9 to the broken lines identified by the circlednumetals 1, 2', 3', etc.

To avoid confusion on this point, it is to be emphasized that neitherthe quality of the atomization, nor theconsumption of the atomizingmedium, depends on the D/d ratio. However, with ratios of 1.5 or lower,it is considered that therequired supply pressure for the medium becomesprohibitively high. With ratios of 6 or higher, the increase in supplypressure is moderate, but the size of the atomizer itself is undulylarge. For these reasons, it is considered that ratios between 1.5 and 6are preferable for practical applications.

The cylindrical outlet bore is considered an essential part of thisinvention, because it is necessary for the stabilization of the flow.Without the discharge nozzle, the conditions in the region ofatomization would be so unstable that uniform atomization would not bepossible.

In order to avoid excessive conversion of tangential velocity to axialvelocity where the atomizing medium passes from the vortex chamber intothe outlet bore, it is considered essential to provide a substantiallysharp corner with an approximate right-angular orientation. It isconsidered that the degree of sharpness of the corner is a moreimportant criterion than the exact perpendicularity, and in fact it islikely that the operation of the device described herein would not beadversely affected by a small departure from perpendicularity of theorder of 5 or 10, or even more.

If, however, the forward wall of the vortex chamber is a cone with anenclosed angle of considerably less than 180, for example from 30 tothen the dominant velocity component in the vortex chamber will be anaxial one, and this will be the case even more so in the outlet bore,resulting in a very narrow angle spray which would not produce arecirculating type of pattern in the combustion chamber. Furthermore,because of the higher axial velocity, the flow rate of the atomizingmedium would have to be significantly higher to provide an acceptablelayer thickness around the inside wall of the outlet tube at itsdischarge end.

Since this invention relates essentially to an atomizer utilizing ahigh-pressure medium, it is particularly adapted for use withhigh-pressure steam. In most burner installations, either compressed airor steam is used for the atomization of heavy oil fuels. Of these two,steam is the most common for economic reasons. In the generation ofsteam, the largest portion of the required energy (heat) is used for theevaporation of the water, and the pressure of the steam requires only asmall portion of energy by comparison. For example, to generate 1 poundof steam (100% quality) at 5 p.s.i.g. requires 976 B.t.u.s, While thegeneration of 1 pound of steam at 75 p.s.i.g. requires 1,005 B.t.u.s.

Since the atomizer discharges steam of 100% quality, the energy releasedby the steam as its expands to atmospheric pressure is highly dependentupon the steam pressure. For example, 5.7 B.t.u.s per pound is availablefrom 5 p.s.i.g. steam and 35 B.t.u.s per pound is available from 75p.s.i.g. steam.

'To illustrate this point in a slightly different way, atomizationenergy of 100 B.t.u.s can be derived from either (a) 17.5 pounds of 5p.s.i.g. steam, generated at the cost of 17,100 B.t.u.s of heat, or

(b) 2.85 pounds of 75 p.s.i.g. steam, generated at the cost of 3,000B.t.u.s of heat.

It is obvious from the above that the use of highpressure steam is farless costly than the use of lowpressure steam. The use of low-pressuresteam for atomization is justified only if it is available at virtuallyno cost (such as, for example, the 50 p.s.i.g. turbine exhaust).

What we claim as our invention is:

1. A liquid atomizer comprising:

means defining a substantially cylindrical chamber having a forward endwall and a rearward end wall,

a cylindrical outlet nozzle defining at least part of said forward endwall and having an outlet bore of diameter less than that of saidchamber and extending co-axially away from the chamber, the forward endwall and the outlet bore meeting to define a substantially sharp corneraround which gas must pass when moving from said chamber into saidoutlet bore,

at least one substantially tangential inlet to said chamber,

means for causing a gas to pass under pressure through Cir said inletand into said chamber so as to set up a rotating vortex in said chamberand along the outlet bore, the said pressure being sufiicient to causethe velocity of the gas at the downstream end of the outlet bore to besubstantially sonic,

and liquid feed means located substantially axially within said outletbore for expelling at least one jet of liquid centrifugally into thevortex where the latter has substantially sonic velocity.

2. A liquid atomizer as claimed in claim 1, in which the downstream endof the outlet tube has an outward conical flare in the downstreamdirection.

3. A liquidv atomizer as claimed in claim 1, in which a ratio D/ d isgreater than 1.5, where D is the internal diameter of the cylindricalchamber,

and d is the internal diameter of the outlet bore.

4. A liquid atomizer as claimed in claim 1, in which said liquid feedmeans comprises a feed tube which extends from a liquid sourceco-axially through said cylindrical chamber and into said outlet bore toa point adjacent the downstream end of the outlet bore, the downstreamend of the feed tube having at least one jet port for expelling said jetof liquid centrifugally into the vortex.

5. A liquid atomizer as claimed in claim 4, in which a ratio D/ d liesbetween 3 and 4, where D is the internal diameter of the cylindricalchamber,

and d is the internal diameter of the outlet tube.

References Cited UNITED STATES PATENTS 1,476,774 12/1923 Simon 239-4063,254,846 6/1966 Schreter et a1. 239-400 FOREIGN PATENTS 879,224 10/1961 Great Britain.

488,312 12/1953 Italy.

LLOYD L. KING, Primary Examiner U.S. Cl. X.R. 239425, 426

